6-furfurylaminopurine (kinetin) is a compound that belongs to plant hormone group called cytokinins. Cytokinins are structurally N6-substituted adenine derivatives. Kinetin was discovered in 1950s and considered to be a growth regulator because it positively influenced the growth of tobacco callus cells. Exogenous application of kinetin induces cell differentiation and morphogenesis of the cells of plant callus and postpones the senescence of leaves. Except for the influence on plant cells, it shows also effects on animal cells. Kinetin possess antioxidant properties and is able to protect against oxidative stress—it is able to inhibit oxidation and damage of proteins, to influence the growth of keratinocytes and to delay aging of human skin fibroblasts in vivo although the compound does not influence proliferation of these fibroblasts. Kinetin derivative 6-furfurylamino-9-(2-tetrahydropyran-2-yl)purine (trade name Pyratine) that is currently commercially used in cosmetic preparations, was prepared by merging protective tetrahydropyranyl group with the kinetin molecule. This structural modification led to the improvement of anti-senescent and antioxidant effects on plant and animal cells including the tests performed on human skin or human skin models.
In recent years, increasing amounts of UV radiation (particularly the secondary (UVB) and long (UVA) wavelengths) reach the Earth's surface. This is a new phenomenon that contributes to the development of a number of skin diseases and disorders in humans. UVB radiation forms about 4-5% of the total radiation and is able to penetrate the skin and the epidermis, where it causes direct and indirect adverse biological effects. UVA accounts for 90% of the total proportion of radiation and penetrates deeper into the papillary dermis and partially into the hypodermis (10%), which causes the formation of reactive oxygen species (ROS) and reactive nitrogen species (RNS). Chronic skin exposure to UVA radiation can lead to premature aging of the skin, which is associated with structural damage of the dermis, resulting in the formation of wrinkles, moles and other signs of skin aging. Natural endogenous photoprotective agent is melanin, but it is not formed in sufficient amounts in human skin, particularly in relation to increasing intensity of UV radiation reaching the Earth due to ozone depletion in the atmosphere and lifestyle modifications (more outdoor activities, clothing that covers smaller part of the body surface). If the skin is treated with a substance which prevents penetration of UV rays in particular, it can protect against premature aging but also against short term adverse effects of UV radiation. Majority of products currently used in cosmetics to protect against solar radiation are so-called sunscreens (UV filters). These sunscreens were developed to protect skin primarily against “harmful” UVB radiation which may give rise to malignant melanokarcinoma. Sunscreens are divided into preparations with physical mechanism of action (inorganic minerals that create a physical barrier to radiation on the skin, such as TiO2 or ZnO) and preparations with chemical mechanism of action (organic substances capable to absorb the radiation by changing the distribution of electrons—for example benzophenones, cinnamate, salicylate). For some existing sunscreens, adverse reactions associated mainly with photoallergic or fotoirritating reactions have been reported when using these products. A common problem of these substances is also photo-instability.
The present inventors found a compound which unexpectedly combines antisenescence effects and UV-photoprotective effects (against both UVB and UVA radiation). These substances are very stable, they are not phototoxic and they do not irritate treated skin.